The present invention relates to an improvement for a wire guide device for a wire electrodischarge machine.
As is well known, a wire electrodischarge machine has wire guides above and below a workpiece in confrontation with each other. A wire electrode is passed through and guided by the wire guides, a pulsative discharge is generated while a machining fluid, such as water or oil, is fed to the minute gap between the wire electrode and the workpiece, and the workpiece is cut and machined into a desired shape as the wire electrode and the workpiece are moved relative to each other. The upper and lower wire guides for guiding the wire electrode are formed of die members consisting of diamond or some other very hard material, so that the wire electrode is guided with precision. Because the wire electrode and the wire guides are cooled by the machining fluid, and the machining fluid must be jetted to form a column enveloping the wire electrode, the wire guides are precisely supported in the wire guide devices.
Configuration of a prior-art wire guide device of this type will be described with reference to FIG. 11. FIG. 11 shows the one disclosed in Japanese Patent Application Kokai Publication No. 182725/1986, and shows a lower wire guide device. An upper wire guide device is similar. In the figure, reference numeral 1 denotes a holder member, which normally comprises a guide holder 1a having a wire guide 3 in the form of a die for causing the wire electrode 2 to pass through its center precisely and thereby to guide the wire electrode 2, and a holder integrally coupled with the guide holder 1a by means of a screw 1c. An insertion path 4 for the wire electrode 2 is provided in the axial center of the holder member 1. The wire guide 3, a feeder 5 for contacting and electricity-feeding the wire electrode 2, a set screw for fixing the feeder 5, and a second wire guide 7 provided on the set screw 6 form part of the insertion path 4.
Reference numeral 8 denotes a housing, having a holder engagement part 8a for the holder member 1. The holder member 1 is inserted in the engagement part 8a. With a tapered surface 1d provided on the guide holder 1a being in intimate contact with a confronting tapered surface 8b of the guide holder 1a, the holder member 1 is mounted. The holder member 1 is fixed by bolt 9 to the housing 8.
Reference numeral 10 denotes a hollow cap fixed to the housing 8 to cover the tip of the holder member 1, i.e., the guide holder 1a. The cap 10 has a jet aperture 10a for permitting a machining fluid to be jetted coaxially. The space inside the cap 10 forms a supply chamber 10b for supplying a machining fluid via conduits, not shown, extending through the housing 8.
Operation will now be described. The wire electrode 2 is guided by the wire guides 3 disposed above and below the workpiece and confronting each other, and is continuously fed from above to below at a constant speed. The machining fluid is supplied through conduits, not shown, to the supply chambers 10b in the upper and lower caps 10, to cool the wire guides 3 and the like, and is jetted through the jet apertures 10a of the upper and lower caps 10. The machining fluid from above the workpiece is jetted forming a fluid column enveloping the running wire electrode 2, therby filling the minute machining gap. The machining fluid from below the workpiece covers the machining part and rebounds. The wire electrode 2 is kept in contact with the feeder 5 and is thereby energized, so that pulsative discharges take place across the minute machining gap between the wire electrode 2 and the workpiece under the presence of the machining fluid. By moving the workpiece and the wire electrode 2 relative to each other two-dimensionally, the workpiece can be cut and machined into a desired shape.
In such a wire-cut electrodischarge machine, the wire guide 3 must be capable of preventing deformation during machining, and must be capable of moving precisely in accordance with the commands from the NC (numerical control) device during taper machining. For this reason, the wire guides 3 are held rigidly by the housing 8 and the holder member 1.
In the prior art, the wire guide 3 is fixed in the guide holder 1a, and the guide holder 1a is fixed to and thereby integrated with, by means of a screw 1c, the holder 1b having the feeder 5 mounted therein, and the integrated holder member 1 is inserted in the engagement part 8a such that the tapered surface 1d of the guide holder 1a is in intimate contact with the tapered surface 8b of the engagement section 8, and is fixed to the housing 8 by means of bolt 9.
A problem associated with the prior art machines is that, in a long-time continuous machining, and mold machining, it is necessary to overhaul, inspect and exchange the wire guides and other members for the following three reasons. The first reason is that the wire guide 3 has a very small clearance relative to the diameter of the wire electrode 2, so the wire guide 3 may be clogged by sludge, or chips of the wire electrode 2 in a continuous operation, necessitating cleaning. A second reason is that the feeder 5 being in contact with the wire electrode 2 may be worn out through a long-time machining, necessitating exchange with a new one. A third reason is that the wire guide 3 may be exchanged so that the wire guide 3 most suitable to the diameter of the particular wire electrode 2 is used.
In the prior art method of mounting the wire guides, it was very difficult, or it took a lot of trouble or a long time to restore the same machining precision after the overhaul, inspection, exchange, etc. First, explanation is made in connection with the first reason, i.e., the cleaning to remove the clogging. To remove the guide holder 1a, the bolt 9 must be loosened, and the holder member 1 integral with the holder 1b must be pulled out of the housing 8. The guide holder 1a and the holder 1b must be disassembled, and cleaned as required, and then assembled, and then inserted in the housing 8, and fastened by the bolt 9. In such a case, the original position of the wire guide 3 is rarely restored. The reason is that the regulation of the holder member in the axial direction is achieved by the taper surface 1d, but there is no regulation on the circumferential direction (rotational direction) of the wire electrode, so if there is a shift in the rotational direction during the mounting of the holder member 1, depending on the pressing force of the bolt 9, abutment between the taper surface 1d and the taper surface 8b of the housing 8 will not be uniform. For this reason, the path for the wire electrode 2 is not in alignment between the wire guides 3 provided above and below the workpiece. For instance, as shown in FIG. 12, if the lower wire guide 3 is shifted to the position 3C relative to the upper wire guide 3a, the path for the wire electrode 2 is shifted by S mm from the original position, and if the machining is conducted in this condition, the precision is poor. It is therefore necessary to examine whether the original inclination of the wire electrode 2 is restored.
As regards the exchange of the feeder 5 for the second reason, adjustment of the inclination of the wire electrode 2 is necessary as above, and time for removal and mounting is required and the adjustment of the inclination of the wire electrode 2 is additionally required. Moreover, even if the adjustment of the inclination of the wire electrode 2 is conducted. it is very difficult to attain or "reproduce" the orginal position precisely.
As regards the exchange of the wire guide 3 for the third reason, it is very difficult to align the center of the wire guide 3 with the axis of the guide holder 1a. For this reason, when the wire guide 3 is exchanged for one with a different diameter, it is necessary to conduct the adjustment of the inclination of the path for the wire guide 2.
The second problem is the insertion of the wire electrode into the lower wire guide. This is particularly serious where, in preparatory works or the like, the wire electrode 2 is automatically inserted, together with a column of a machining fluid jetted from the jet aperture 10a of the upper cap 10, in the lower wire guide 3. The reason is that the fluid column is introduced in the lower cap 10 and rebounds toward the axis of the wire electrode 2, and the column is disturbed because of the interference due to the rebound, creating troubles in the automatic insertion of the wire electrode 2.
A technique for preventing disturbance of the column of the machining fluid that has been generated normally is disclosed for example in the above-mentioned Japanese Patent Application Kokai Publication. However, this technique relates to the stage prior to the introduction of the disturbance of the column into the lower cap, and it does not solve the problem of disturbance of the column due to the rebound within the cap after the introduction.
The third reason is connected to the first reason, and relates particularly to the removal of the deposit near the lower wire guide. Such deposit can cause disconnection of the wire electrode 2, and must be removed from time to time. In a prior art, a structure in which a machining fluid is made to flow around the wire guide 3 is known, for example from Japanese Patent Application Kokai Publication No. 115126/1984 and Japanese Patent Application Kokai Publication No. 156623/1984. In the former publication, a plurality of openings for the passage of the machining fluid are provided between the wire guide 3 and the die holder of the guide holder 1a. In the latter publication, the guide holder 1a having the wire guide 3 is mounted within the nozzle main body (corresponding to the cap 10 in FIG. 11), and a multiplicity of openinigs are provided around the mounting part for the wire guide 3 in the guide holder 1a, so that machining fluid flows from inside the guide holder 1a, through the openings into the nozzle main body. In the former case, the holding force of the wire guide 3 is lowered because of the openings provided on the die holder, and the pressure of the machining fluid may displace the wire guide 3. In the latter case, there is no such possibility, but it is necessary to provide a multiplicity of openings in the guide holder 1a uniformly, so it is complex.